The propulsion system of some skid steers has an engine which powers two independently operable drive mechanisms, one drive mechanism for the front and rear wheels on the left side of the vehicle and the other drive mechanism for the front and rear wheels on the right side of the vehicle. Each drive mechanism has a hydrostatic transmission, a chain drive, a final drive for front wheel, and a final drive for the rear wheel.
With respect to each drive mechanism, the transmission has a variable displacement pump, configured to pump hydraulic fluid in opposite directions, and a bi-directional fixed displacement motor that receives hydraulic fluid from the pump. The output shaft of the motor operates the chain drive located inside a chain case. The chain drive has a pair of chains, each chain being driven by a sprocket mounted to the motor output shaft. One chain drives the final drive associated with the front wheel, and the other chain drives the final drive associated with the rear wheel.